Method and moulding tool for manufacturing fibre-reinforced products

ABSTRACT

A method and apparatus for manufacturing fiber-reinforced products with integrated insert parts by moulding a heat-bonding resin having a viscosity of about 1-10_6 and about 30-10+6 mPas, between two joinable halves of a separable mould having an upper and lower mould parts forming a cavity therebetween, the inner moulding faces are attached to displaceable fixed parts of a pressing table. Prior to moulding, an insert part is fixed in position in the cavity, and the mould parts each have a set of a support devices displaceable in the cavity relative to the respective moulding faces. According to the method, the resin is located in the cavity before the mold is closes and the insert is in position prior to and during an initial phase of moulding. The support device is removed prior to the setting of the resin in the mould leaving holes in the material, and thereafter the mold parts are held together for filling the holes.

TECHNICAL AREA

The present invention relates to a method for manufacturing products offibre-reinforced thermosetting plastic with integrated insert parts bymoulding a heat-bonding resin between two joinable halves of a separablemould, whereby the insert part is fixed in position in the mould cavitythat is demarcated between the two joinable halves of the mould prior tothe moulding of the product. The invention also relates to a mouldingtool for carrying out the method.

THE PRIOR ART

The manufacture of moulded goods where the starting material essentiallycomprises reinforced plastic material takes place through apredetermined amount of moulding material of a heat-bonding resin beingpressed between two steel moulds at temperatures that commonly lie inthe range 140-165° C. The moulding is commonly performed in hydrauliclow pressure presses where the moulding pressure can be regarded asbeing relatively low and in general not exceeding 5-20 MPa per projectedarea of the moulded goods. The cavity is defined by the recessed facesof the two joinable mould halves in the form of an upper part and alower part that are commonly made of machine tool steel and havingcarefully designed cutting or compression edges whose task is to sealthe cavity and cut off any eventual excess material. The process cycletimes of the compression moulding process depend on the properties ofthe chosen staring material and the design and complexity of the productin general, but can generally be regarded as relatively short and seldomexceeding 2 minutes. The moulding material that is used for the mouldingcommonly includes a type of material pre-impregnated with resin, forexample, in the form of pre-impregnated fibre structure, so-calledpre-pregs. The said pre-impregnated material is commonly designated“Sheet Moulding Compounds” and in the following is given the termSMC-material. In certain applications, there is a need to manufacture bycompression moulding highly resistant products whereby specific detailsor so-called inserts are wholly or partially incorporated in andenclosed by the SMC-material. In particular, it has been shown to bedesirable to be able to manufacture products of SMC-material withincorporated and essentially enclosed electrical or electroniccomponents in the form of circuit boards or similar within them.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to achieve a method that makes itpossible to use compression moulding to manufacture details in which theinserts are incorporated in and essentially enclosed by the mouldingmaterial. In particular, it has been shown to be desirable to be able tomanufacture products of SMC-material in which electronic components inthe form of circuit boards or similar are incorporated in andessentially enclosed by the said SMC-material. Another aim of theinvention is to achieve a moulding tool to perform the actual method.

These aims are achieved by the method and device according to thisinvention having the characteristics stated in the independent claims 1and 5 and, more specifically, by the method according to the inventionbeing in principle characterised in that during moulding, mouldinghalves each having a set of support devices are displaceable in aprojecting manner relative to the moulding face associated with eachmoulding half, that the insert part is held in a fixed position betweenthe said support devices prior to and during the initial phase of themoulding, that the supporting devices are removed from their positionsupporting the insert part before the resin sets in the mould, and inthat the mould halves are further pressed together during the fillingout of the holes left after the support devices, whereby the materialthat is used during the moulding is given a certain excess volume thatis equivalent to the volume of the said holes.

DESCRIPTION OF THE FIGURES

In the following, the invention is described in greater detail withreference to the following drawings, in which:

FIG. 1 shows in perspective view an x-ray image through a so calledbalis-plate, which is used as an example of one embodiment to describethe principle that forms the basis of the present invention,

FIG. 2 shows a longitudinal view along the line II-II in FIG. 1,

FIG. 3 shows in the form of curves a diagram of the time and workingprocedures when compression moulding an SMC-material in a conventionalhydraulic moulding device as well as the cycle of operations whenmanufacturing an equivalent product of SMC-material with an insert partincorporated in and enclosed by this according to the principles forthis invention.

FIGS. 4 to 9 show fragmented views, partly in cross-section, of thedifferent steps of the manufacturing process according to the invention.

DESCRIPTION OF ONE EMBODIMENT

The balis-plate shown in FIGS. 1 and 2 and generally designated 1 ismade from an SMC-material and is incorporated as a part in a so calledATC-system (Automatic Traffic Control) that is used for the automaticsupervision of trains. The said balis-plates lie attached to sleepersbetween the rails that form the rail track, ad their task is to registerand transfer information about passing trains to and from the computerunits with which the locomotives are equipped. With the help of thisinformation, the computer unit of the locomotive can, among otherthings, calculate its location on the track and confirm the whereaboutsof other trains. The information transfer from the balis to thelocomotive or vice-versa takes place in a wireless manner, whereby thebalis is equipped with a means of transmission, including an electroniccircuit that via a first 2 and a second connection point 3 is inelectronic communication with an antenna loop 5 arranged on a circuitboard 4, where this is embedded in the moulding material that forms thestructure or body of the balls. The balis has a predetermined orexpected operational life span and it should be realised that theability to prevent moisture and fluids from forcing their way into thesensitive antenna loop 5 is critical if this set life span is to beachieved. At the same time as the balis-plate 1 is at the mercy of theelements through its location between the rails, i.e. it is very exposedindeed, very great demands are made on its reliability and functionsince the balis-plate is part of a safety system. Not the least, itshould be realised that the effective embedding of the antenna loop inthe moulding material contributes to raising the operational reliabilitysince fluids and moisture are prevented from coming in contact with thesaid antenna loop.

With reference to FIGS. 4-9, a moulding tool intended for manufacturingthe balis-plate 1 as shown in FIG. 1 with the loop-shaped circuit board4 embedded in it is shown. The moulding tool includes two joinable mouldhalves comprising an upper mould half 6 and a lower mould half 7 that ina known manner can be assembled in a releasable manner at the upperdisplaceable 8 and lower fixed 9 parts of a pressing table indicated bya dashed/dotted line and included in a figure but not illustratedfurther. In each case, the two joinable mould halves have a mouldingface or a working surface 10 respective 11 that, when the mould halvesare joined together, demarcate an inner cavity that is equivalent to theouter shape of the balis-plate 1. The cavity formed by the said mouldhalves 6, 7 is preferably of the so-called sealing type and designed inthe known manner so that when the halves are clamped together, only asmall amount of moulding material is pressed out through the gap that isdemarcated between the parting line of the mould halves.

The moulding device also has an associated control and guidance device,not shown in the figures, for example, a programmable computer orsimilar, with whose help all the parameters necessary for performing thecompression moulding operation, including amongst others the sealingspeed of the moulding halves, the temperature, the different directionsand cycle times of the process, plus associated equipment such as thedriving cylinders, etc., can be controlled and guided.

The upper respective lower mould halves 6, 7 each include a set of thesupport devices 12 that, when acted on by an adjusting and manoeuvringdevice 13, are displaceable in a projecting manner relative to themoulding face 10 respective 11 to, in their forwardly projectingposition, be able to grasp hold between themselves of the insert partthat, in the form of a circuit board 4, is to be accommodated in theproduct made from the SMC-material. To be able to grasp hold of thecircuit board 4, the support device 12 at each of the said mould halves6, 7 includes a set of support pins 14 where each of the ends that facesin towards the cavity is directed at one another, and where the supportpins are able to run freely into and out of the cavity by beingaccommodated in a sliding manner in holes 15 arranged in the mouldhalves. In general, it can be said that the number of support pins 14,their configuration, and their position relative to one another ischosen on the basis of the contour and shape of the insert part that theprojecting support pins are to grasp between themselves. Theconfiguration of the product otherwise, such as its degree ofresistance, etc., naturally also makes demands on the design of thesupport pins 14. In this description of one example of an embodiment,the support pins 14 are configured so that they exactly follow theloop-shaped and essentially plane outer contour of the circuit board 4.

At their ends that face away from the cavity, everyone one of the saidsets of mutually facing support pins 14 is joined to the unit by arespective element 16 in the form of a slab that is located within aspace that is limited by the associated mould half 6, 7 and anattachment device 17 for attaching the mould halves 6, 7 to the pressingtable 8, 9. Axles 18, on which the slab 16 is displaceable in a guidedvertical direction within the said cavity, extend between the saidrespective mould halves 6, 7 and the associated attachment device 17 forthe releasable attachment at the pressing table 8, 9. The adjusting andmanoeuvring device 13 named above controlled by the computer-controlledcontrol and guidance device named above is used to manoeuvre the slab 16and thereby also to execute the movement of the support pins 14 relativeto the moulding face 10, 11 associated with each mould half 6, 7. Theadjusting and manoeuvring device 13 is designed so that the support pins14 can be manoeuvred freely into and out of the cavity and be pressedwith a chosen constant pressure against the circuit board 4 accommodatedbetween the mutually facing support pins 14 independently of thelocation of the mould halves 6, 7 relative to one another. The adjustingand manoeuvring device 13 with the properties named above is alreadywell-known and will not be described in more detail in the following,but it does suitably include some type of pneumatic or hydraulicallyacting piston-cylinder device with an associated system of flow pathwaysand components. The adjusting and manoeuvring device 13 can preferablyinclude a set of hydraulic cylinders 19 whose respective ends are joinedwith the slab 16 respectively the attachment device 17 and that, inorder to be adjustable with a variable force, are, in a known manner,connected to a hydraulic circuit that includes among other things sometype of pressure-controlling valve device in the form of, for example, aso-called flow regulator or similar. In what is a per se well-knownmanner, a set of ejection pins 20 whose task is to eject the finishedproduct is arranged at the lower mould half. Since the said ejectionpins 20 are already well-known, their function or construction designwill not be described in detail, but it is appropriate that the ejectionpins 20 and support pins 14 in the lower mould half are arranged forsimultaneous manoeuvring and common ejection of the finished product.

With reference to FIG. 3, the continuous line in the diagram shows acurve of time and working procedures during a typical cycle ofoperations when compression moulding a SMC-material in a conventionalhydraulic moulding device. The dotted/dashed line in the same diagramshows a typical curve of time and cycle of operations when manufacturingan equivalent product of SMC-material with an insert part incorporatedin and enclosed by this according to the principles for this invention.

With reference to the continuous lines, the operational steps begin withan SMC-material 21 being loaded into the mould; A, where after the mouldis closed; B and the material is brought to flow until the mould iscompletely filled and under pressure; C, the material 21 undergoesthermosetting; D, where after the mould is opened; E and the productformed from the SMC-material is removed; F.

In accordance with the principles of this present invention, the dashedline in FIG. 3 shows the time and working characteristics for a cycle ofoperations for manufacturing products from SMC-material with an insertpart integrated in the moulding material. The different operationalsteps for manufacturing the balis-plate 1 exemplified here with acircuit board 4 integrated in the moulding material are described belowwith reference to the dashed line in the diagram plus the series ofdrawings in FIGS. 4-9.

As is shown in FIG. 4, with the upper 6 and lower 7 mould halves locatedin their open position and the said set of support pins 14 located intheir projecting position relative to the moulding faces 10 respectively11 of the form halves, the circuit board 4 is placed in a restingposition on the free ends of the support pins 14 in the lower mould halfand a specified amount of SMC-material 21 is loaded into the mould; A′.As is normal when determining the amount of SMC-material required forcompression moulding in so-called positive moulds, the amount loaded hasbeen given a certain excess volume and in addition has been given anexcess equivalent to the volume for both sets of support pins 14 whenthey project into the sealed mould in their extended positions. In FIG.5 and step B, the mould is sealed, whereby the circuit board 4 is fixedin position with a constant, predetermined clamping force between bothsets of support pins 14. Following this, the SMC-material is brought toflow until the cavity is completely filled, C′. To facilitate theflow-out and to thereby avoid the risk that the circuit board 4 fixed inposition between the support pins 14 be deformed, the speed of sealingof the mould and thereby the filling out phase are significantly longerthen the speeds normally applicable for compression moulding ofSMC-material without insert parts. An appropriate speed for the currentexample is about 1 mm/second or less than this said speed, which, inthis example, would mean that the filling phase is at least 20-30 timeslonger than normal. This should be realised by comparing both lines Crespectively C′-C′ in the diagram, and in this respect lies thedifficulty of giving the moulding material such a mix and propertiesthat it does not set during the relatively long closing and sealingtimes of the mould.

In the embodiment described here, the closing times are about 1 minute,which contrasts with the closing times that normally apply whenmanufacturing equivalent items without an insert part when the closingtimes normally hardly reach 2-3 seconds. In this respect, theflowability of the SMC-material has been significantly reduced inrelation to the degree of flowability that normally applies whenmanufacturing equivalent items without an insert part, but theSMC-material does not become unmanageable because of this. In addition,the addition of so-called inhibitors, i.e. substances that delay thechemical reaction, also ensures that the SMC-material does not setduring the sealing of the mould. During the manufacture of a balis-plate1 with a shape equivalent to the embodiment described, SMC-material 21having a degree of flowability in the range 1·10⁶-30·10⁶ mPas(millipascals per second, according to the Brookfield Viscosity meterwith a spindle T-F/1 rpm) has been shown to give a very good result Adegree of flowability around 5·10⁶ mPas has been shown to be preferable.

As the support pins 14 occupy a part of the total volume in the cavitydemarcated between the mould halves 6, 7, the closing process of thecompression moulding operation according to the invention, with regardto the working motion, is ended somewhat earlier than normally would bethe case with the compression moulding of SMC-material. This should beclearly evident from a comparison of the dashed line and the continuousline in the diagram at the points C′ respective C. In this respect, themould halves 6, 7 have been given a vertical parting line with narrowtolerances so that an effective sealing between the interacting partscan be obtained at the closing of the mould halves, despite the lowdegrees of flowability chosen for the moulding material in this case. Itshould be pointed out that the low degrees of flowability for theSMC-material 21, in combination with the narrow tolerances and lowdegree of play of the parting line or the compression edges, place highdemands on the guiding of the mould halves 6, 7 relative to one another.In the present embodiment, with its selected degrees of flowability, ithas been shown to be appropriate to use mould halves whose compressionedges have a gap with a play in the order of 0.05-0.08 mm when the toolis closed.

With reference to FIG. 3 and FIGS. 6 and 7, the SMC-material is pressedtogether and brought to flow and fill out the mould; C′, whereby, beforethe material sets, the support pins 14 are manoeuvred out from thecavity and thereby away from their location grasping the circuit board 4(FIG. 7), after which the mould halves 6, 7 are further pressed togethersomewhat during the filling out of the holes left after the support pins14; R′. Finally, the material undergoes setting during a specifiedinterval of time D′-D′.

It can be pointed out that even if the interval of time chosen is guidedby a series of design factors such as the thickness of the goods and theshape of the product the chosen setting time is significantly longerthan what is normally used and in this described embodiment is up to 12minutes. The said relatively long setting time is symbolised by thebroken line between the points D′-D′ in the diagram. In the final phaseof the moulding and in the compression phase, no material in principlepasses out through the compression edges of the mould halves 6, 7.

When the SMC-material has undergone the setting required, the mouldhalves 6, 7 are opened; E′ (FIG. 8), after which the finished productor, more specifically the balis-plate 1, is ejected by means of theejection pins 20 and removed from the mould; F′ (FIG. 9).

The present invention is not limited to that described above and shownin the drawings, but can be changed and modified in a number of wayswithin the scope of the concept of the invention as specified in thefollowing claims.

1. A method for encapsulating an insert part comprised of afibre-reinforced circuit board having circuit components mounted thereonby compression moulding a heat-bonding thermosetting resin about theinsert part between two joinable halves of a separable mould, said mouldhaving an upper mould half and a lower mould half forming a cavitytherebetween when the mould is closed, inner moulding faces attached todisplaceable respective fixed parts of a pressing table, wherein, themould halves each have a set of a support devices displaceable in thecavity relative to the respective moulding faces comprising the stepsof: selecting the heat-bonding thermosetting resin having a viscositychosen in the range of about 1-10⁶ to about 30-10⁶ mPas; positioning thesupport devices in the mould for supporting the insert part in a fixedposition relative to the mould faces; positioning the insert part on thesupport devices; thereafter loading the heat-bonding thermosetting resinin the mould; closing the mould after the loading step and thepositioning step; pressing the mold halves together for compressing theresin to initiate curing of the resin after closing the mold;concurrently with compressing the resin and prior to curing of theresin, removing the support device from its position supporting theinsert part leaving temporary holes in the material; and thereaftercontinuing pressing the mould halves together to further compress theresin for filling the temporary holes left in the material after removalof the support device and to continue the curing of the resin until saidresin fully cures, whereby the circuit board and electronic componentsthereon are surrounded by the fully cured resin without damaging thecircuit board and electronic components.
 2. The method according toclaim 1 further including the step of giving the resin a certain excessvolume equivalent to the volume of the holes left after the supportdevice is removed.
 3. The method according to claim 1 further includingthe step of placing the insert part in a resting position on the supportdevice of the lower mould half located in a forward projecting positionrelative to the associated mould face, and during the sealing movementof the mould, the support devices of the upper mould half, after contactwith the insert part, are displaced into the upper mould half duringexertion of a constant force of pressure against the insert part.
 4. Themethod according to claim 1, including selecting flexability of 1·10⁶mPas of the thermosetting resin.
 5. The method according to claim 1,including selecting a heat-bonding thermosetting resin comprising one ormore inhibitors for delaying the chemical reaction during the sealing ofthe mould.